My fp refuses to stop being “homies” with someone he was in a short term relationship with between the times we were together.

Tl;dr my bf of 3 years and I broke up for 6 months a year into our relationship and he attempted to have a relationship with someone else in that time while he was trying to move on and now they are still friends and apparently talk 2-3 times a week on the phone. She tried controlling his and I’s friendship during that time but I refuse to do the same to her. I’m still in so much emotional pain 2 years later that I’m contemplating if it’s even worth it. We have been planning on marriage and a future together. What can I ask him to do for me or what do I have to do to be okay with this? Do I need to be okay with this?

My boyfriend and I were together for a year, then broke up because I didn’t know I had bpd at the time and I got scared of the commitment and how much I liked him.

Then my heart was torn apart for months. I didn’t believe we had broken up, but he tried to move on and it hurt very badly. A few months later he started dating someone he matched with on tinder and they dated for ~2 months. During that time I once asked him to stop by on his way to her house because I was struggling for a will to live and I was completely broken down and in deep emotional pain and he consoled me for a couple hours. We have always stayed friends. While they were together though, she asked him to always get permission before hanging out with me and seemed to really dislike us still being friends, probably sensing how close we were and wanting to keep him for herself.

I went to ED treatment and left early because I had no one to emotionally support me. When I got home, the first thing my therapist did was diagnose me with BPD (with lots of discussion and she at that point knew my history). Around this time, him and her broke up because he says he never came to finding her attractive, that they just clicked really well (he has antisocial personality disorder so he doesn’t really bond with anyone within such a short time frame).

Me and him began rebuilding our friendship and it’s been almost two years since we’ve been back together. We are cautiously planning our future together and view our time apart as a solidifier that we do really love each other and want to be together.

However, he has also maintained his friendship with her. I don’t do what she did to me and I let him have his autonomy with his social circle. Also however, recently I have been finding out things he’s never told me, like that they had hooked up while they were together even though he told me it takes months to be able to build himself up to actually enjoying sex (demisexual-esque) and that they broke up because he never got into her so when I found out that he kept it from me he said it was because he knew how upset I’d get and that he actually doesn’t remember not telling me (it literally just slipped out of him recently).

He had a kinda meltdown about how, with his disordered antisocial tendencies, he usually tells lies to coax a situation into being more comfy for him and protecting the feelings of others, and had never been caught in a lie before. I asked him to stop doing that to me and he is trying very hard to be honest to me about things now.

Then the other day I found out he’s calling her pretty frequently because she’s in town. He always told me that they weren’t close and then after I confronted him about it, he said they were “homies” and she’s the first person he could be basically sociopathic with without fear of judgment.

I know I’m in an abnormal relationship, but it really works for me because A) he does not react to my bpd traits like at all and is very open to trying to understand me, like he knows my actions and words are commonly based on big feelings, and B) for him we relate a lot on antisocial behaviors and so for us both we feel we are able to truly be ourselves around each other in a very real way with wide-open communication (except this issue apparently).

I really am not coping well with this friendship he has after all this time and I’m seriously considering cutting him off entirely despite everything we have built and been through. I didn’t know they were so close or that they talked on the phone. Every time he hangs out with her, or talks to her, it rips open a huge wound on my heart over and over again, and idk if our connection is worth the pain.

Idk what to do. Idk if asking him to stop their friendship is the right thing to do or if I should just go back to therapy to try and feel ok with it. I’ve told him our relationship is at stake and his reply was something like “I need you to tell me exactly what is and isn’t appropriate” and I don’t have an answer for that. I want the friendship to be over completely. He said it’s not possible. I can’t even inflict the same pain back to him because of his antisocial/nonchalant personality. I don’t think there’s anything I can do to show him my pain besides this.